Detonation suppression means for internal combustion engines



4 Sheets-Sheet l A. G. BODlNE, JR

March 20, 1956 DETONATION SUPPRESSION MEANS FOR INTERNAL COMBUSTION ENGINES Filed Feb. 25, 1952 IN VEN TOR. flue-er G. Boo/Male.

udzfarny March 1956 A. G. BODINE, JR 2,733,732

DETONATION SUPPRESSION MEANS FOR INTERNAL COMBUSTION ENGINES Filed Feb. 25, 1952 4 Sheets-Sheet 2 INVENTOR. 41.5522 6. Boom/6J3 March 20, 1956 A. cs. BODINE, JR 2,738,782

DETONATION SUPPRESSION MEANS FOR INTERNAL COMBUSTION ENGINES Filed Feb. 25, 1952 4 Sheets-Sheet 5 INVEN TOR. 418627 6. Boo/NE 2:

March 20, 1956 gamma, JR 2,738,782

DETONATION SUPPRESSION MEANS FOR INTERNAL COMBUSTION ENGINES Filed Feb. 25, 1952 4 Sheets-Sheet 4 INVENTOR. flLBL-nf G Boom/fife.

United States Patent DETONATION SUPPRESSION MEANS FOR INTERNAL COMBUSTION ENGINES Albert G. Bodine, In, Van Nuys, Calif.

Application February 25, 1952,, Serial No. 273,277

(Jlaims. (Cl. 128-191) This invention relates generally to internal combustion engines and to means for suppressing irregular burning and detonationof fuel-air mixture therein. The invention is based on my discovery that detonation in combustion engines involves acoustic phenomena and can be alleviated'by means *of certain acoustic wave suppression apparatus usedin-combination with the combustion chamber.

The present application is directed to improvements in the fi'eld dovered'by my No. 2,573,536, issued @ctober 30, 195.1, antl'entitled Engine Detonation Connot "by Acoustic Methods and Apparatus. The present application is a continuatiominspart of my application Serial "No. 252,818, filed October 24, i951, for Engine Detonation Control by Acoustic Methods; and Apparatus, which latter application is a division of my application Serial No. 234,688, filed July 2, 1951, which resulted in said Patent No. 2,573,536. For a full discussion of the acoustic aspect of detonation in combustion, and my l-basic solution for controlling detonation in combustion, reference'should be had to my said Patent No. 2,573,536.

Only briefly stated herein, the, present invention is based on the fact that detonation in'an enginemombustion chambe'r produces sound waves, a large ,Qfllit .ofwhioh rise to high amplitude at resonant frequencies of the chamher, and on-my discovery that the sound'waves produce "the various 'well known and harmfiul manifestations of detonation. According to my basic invention, I inhibit or attenuate these hanmful effectsbyinterfering with or attenuating the high-amplitude detonation-induced sound waves, and this is done by use inconnection with the combustion chamber'of 'acousticzattenuation means made responsiveto theifrequencies at which the detonationindueed sound waves build up to high? amplitudes.

Theageneral-object iofuthe present inventiomis the provision of an impr ovedttype of "acoustic attenuator, combined -with-=thc combustion .chamber of an internal combustion engine, and broadly capable of use in" either the fixed walls of the combustion chamber, or the crown of the piston; or both.

A further-object is theprovision of an improved, practieal -form of acoustic attenuator or the combustion chamber walls or piston, havingta broad frequency response -to detonationdnduced sound --waves, and :also so designed asto cover and'bc cflective area large proportion of the acoustic wave patterns whichwteud to be set up within the combustion chamberwhile at the same time "eeing wellcoupled acoustically withzttheiwave patterns, so-that the attenuator-base large effectonrthetdetonation.

In the drawings, --showing certain present illustrative 'embodimen-tsof the invention:

\ Figure 1 is a vertical'longitudinal sectional view'through a cylinderand piston of an internal combustion engine embodying an illustrative form of the invention;

Figure la shows a'modification of aportion of Figure 1;

Figure 2 isa plan view of tho pistonof Figure l;

Figure 3 is a diagrammatic planview of a typical combustion chamber, showing'the location ofuareas of high acoustic impedance;

2,738,782 Patented Mar. 29, [956 Figure 4 is a plan view of an alternative piston in accordance with the invention; I

Figure 5 is a section taken on line 5-5 of Figure 4;

Figure 6 is a transverse sectional view through the block and head of an engine showing still another embodiment of the invention; 1

Figure 7 is a developed view of the horn of Figure 6 in accordance with a curved plane passing through the line 7-! of Figure 6; i

Figure 8 is a bottom plan view of the horn member of Figures 6 and '7;

Figure 9 is a vertical sectional view through a modified piston form of my invention, being taken on line 9-9 of Figure '10; and' Figure 10 is a plan view/d the piston of FigureQ.

In the drawings, Figure 3 is atdiagram showing regions .of high acoustic impedance (pressure anti-node regions) of a typical acoustic standing wave pattern such as may be found in a cylindricalcombustion chamber oftt he overhead valve type. :It ,is .to be understood that such a chamber may have a number of resonant frequencies, a fundamental, and one or more :higher modes, all of which may be driven byone ortmore sources of detonation vwitl iin the combustion flame. Acoustic resonant standingtwave patterns, consisting of superimposedt'fundamental and higher frequency .mode patterns, are thereby set up in the ehambeneach consistirlgof spaced pres'sute nti-ncde-regions 'Q'highacoustic impedance), with interve ting iveloeity tantimode regions t(low acoustic impedsauce). The 1 high irnpedanccarcgions may be located .and v h standing waves lotted tbs/procedures set ifOl'th in my aforem ntione issued iPatc'nt YN0.1213,536. ime fundame tal frequency modetin one dypical .case tFig- ,ure 3) is taunt! :to have twotdiametricallyfloppositethigh nrsedaacw pr ssur reg ons P, ,and theoscillatiugtsa ztiew; a h imerreningwdocityamhnode.region for tthi 1 fundamen al runaway ,is ,alternately lfl'Om t me of theregiops i to theefiihcr aud then in theieverse direction. ,Thefirsuhigher un detconsists otfourthigh unpedauee prpssutetantiquodegregions or sectors, .twoof t his tmay ,ssutsid wi h she 118W Amused ,regifins P, a d: the other F5169 ti fieiflut afl i, aretthenuspaced .bfitweunrthc lzegions i. tAt thehyelocity anti-nodes between ihj5:jQUl;IgiqnS,,-glihe gas t-flowntravels first in en t rsct nt n :ths r h -o h :Th sec nd hi mode is, v atradial mQde having. a; high ;impedance pres- "sur an i'se e tssiemiifai [th entr l ssi ns sh chamri s enisaess rsumfsrenual .bis impe an memori l n -nojieg scmn aroun hetn flphe y of mash-"am er. Betu/een: these regions. is an annular t n it stains her i m i-11mins en :fl tt ke mlas inetat isl si tss iu l e thir th shc -mqd h s hiss mr s sases te su s amped sectors, sp ce 60 from one another tago pf thqse sometimescoincidns i st ',3i9 i t lgmainingsectors, indicated ,at, P3, being d stributed; between, the ,regions tP as in c d Betwe n, i rPtssur anti-node regions. there are, velocity,antpuoderegionsjor th third higher anode, frequency, wherein I :the ggs oscillates at .said fre ,quency.

Csusids ipstauv Pa P (the {o situatio itwill .be, evldentthattthg pressurepyglqamne ptessur tami-node is 1 80,,9ut-0;Qb35q refierenee, to-thepressure cycle ,at an acoust cally posed pressure, anti-node. ilhus, .consideringtthe fun mental reguency mode as illustrative, the pressure cycle at one pressure anti-moduli? is (Moog-phase, with reliere nce to that ,at the opposite pressureanti-nodeP. -fl algingthe first higher, mode as another instance, the presstge ogcle at.anygiyenpressure vfiii-li t t wi h respuytgo higher, mode pressure tcyolesat apart by the spacing distance of two oppositely phased high impedance regions for a given mode of vibration. and are exposed to the chamber in as near coincidence with the said high impedance regions as can be achieved. Since it is sometimes difiicult to locate the high impedance regions of the chamber with accuracy, and since the high impedance regions are somewhat subject to shifting, I prefer to provide a plurality of the passages, at different angular orientations, so that at least one of the passages will have its ends located in near coincidence with the high impedance regions for any condition that may be encountered. These passages are designed to form paths for substantial gas flow between the high impedance regions, in shunt" with the combustion chamber. Gas will oscillate within a properly designed shunt passage between two high impedance points of a standing wave pattern, in response to the 180 out-of-phase pressure cycles at the two high impedance points, provided its length and general configuration make it frequency responsive" to the frequency of the said standing wave.

It is of course well known in acoustics that any pipe is I frequency selective, or frequency responsive, in that there is one fundamental frequency at which it will best conduct sound waves, and consequently, at which gas oscillation within it can be maximized; also, that the response frequency depends on the length and configuration of the pipe. Such a pipe is said to be tuned to the frequency of the sound wave. So here, the gas passage is made of such length and configuration that, by application of ordinary knowledge and techniques of acoustics, the passage is tuned, that is, frequency responsive, to the acoustic standing wave to be controlled. Assuming such frequency response, sound waves will readily pass through the shunt gas passage, and gas oscillations therewithin, owing to the conducted sound wave, will be maximized, or at least established at substantial amplitude. It should be seen that the ideal case would be one wherein the length and dimensions of the shunt gas passage are precisely those giving maximum frequency response to the acoustic wave pattern of which the two pressure antinode regions are a part. In such case, a full standing wave, with at least one intervening velocity anti-node (minimized acoustic impedance) is established in the passage. In practice, it is not necessary that this ideal condition be achieved, and a suflicient approximation, or approach, is made if the passage accepts the sound wave in substantial measure, and a reasonably high velocity oscillating gas flow is established.

The invention involves one further step or feature, the provision of high acoustic resistance for the shunt gas passage, whereby substantial acoustic energy will be dissipated. That is to say, the shunt gas passage is given some suitable energy dissipative configuration, generally speaking, a constriction, or constricting or impeding means, whereby the high velocity gas particles traversing the same will be forced to give up their energy, which is thus lost to the olfensive acoustic wave. In a constricted portion of a gas passage, the velocity of the gas particles is increased, and the high velocity particles scrub against one another and against the walls or passage defining media in such a way as to develop a frictional scrubbing efiect, and much acoustic energy is thus dissipated in the form of heat.

The acoustic wave is attenuated, or prevented from build-up, by thus abstracting and dissipating energy from the oscillating gas flow in the shunt passages. It will be seen that if the passages were left open for free and unrestricted gas oscillation, the kinetic energy periodically imparted to the gas would be returned to or conserved in the acoustic system as pressure energy upon each reversal of gas flow direction. But by causing this energy to be largely dissipated through gas scrubbing action in the shunt passages, the energy of the acoustic standing wave is constantly bled off, and the wave is hence prevented from reaching the high amplitudes at which detonation becomes decidedly harmful. In eifect, the passage is coupled to the high impedance regions of the main cavity by virtue of its frequency response and orientation, with the result that it can extract vibratory energy, at detonation frequency, from the main cavity. It is then only necessary to dissipate this extracted energy in the passage.

Figures 1 and 2 show one illustrative embodiment of my invention, designed particularly for the type of acoustic wave pattern diagrammed in Figure 2, and wherein the sound wave gas passages as mentioned above are provided, first, in the head of the piston and, second, in the head end of the combustion chamber. The engine is a valvein-head type, having a water cooled block 10, water cooled head 11 fastened to block 10, and a piston 12 reciprocable in cylinder 13 within block 10. Head 11 provides a generally domed combustion chamber 15 of cylindrical cross section over piston 12. The block and head are shown with water jackets 16 and 17, respectively, and the head has intake and exhaust valves, one of which appears in Figure 1 at 18, and a spark plug, indicated at 19.

The head 20 of piston 12 has a convex crown portion 21, and formed therein, near the periphery of the piston, are a plurality of angularly spaced flared entrance ports or mouths 22. These entrance ports 22 form the outer ends of gas passages 23 radiating from a centrally located chamber 24, which. in the illustrative embodiment, is packed with a constricting substance, preferably a wad or body 25 of fiber glass. It will be noted that the crowned type of piston permits the use of simple straight passages 23. In addition to the peripheral ports 22. there may optionally be employed a centrally located entrance port or mouth 22a, which communicates with a passage 23a leading vertically downward to the chamber 24. A screwthreaded plug 26 closes an access opening 27 in the bottom of the piston head leading to the chamber 24, and by removing this plug, when the piston is out of the engine, the fibrous packing 25 may be serviced.

The gas passages referred to above are preferably formed with a uniform taper, and the outer ends thereof communicate smoothly with their flared mouths. If desired, the gas passages and flared mouths may have an exponential horn shape, giving large mouth area, maximum acoustic coupling, and conveniently small total volume.

As may be seen from a comparison of Figures 2 and 3, I can have a plurality of these passages, like spokes in a wheel, so that there can always be one entrance opening 20 and passage 23 leading to fiber glass packing 25 sufficiently near to each of the high impedance pressure anti-node regions P, Pi, and P3, even though the wave pattern should shift in orientation.

Usually, the radial mode (second higher mode) will not be overly serious, and can be neglected, in which case the gas passage 23a is omitted. Such omission is sometimes of advantage, since the passage 23a may have a degree of shorting" effect on the passages 23, 23 extending diametrically across the piston. In any case in which the radial mode is predominant, or comparatively serious, the passage 23a can be employed.

It will be recalled that, in addition to the centrally located pressure anti-node I for the second higher mode. there is an annularly distributed pressure anti-node extending around the periphery of the chamber. The several mouths 22 located at pressure anti-nodes P, P1, and Pa,

'5 one also for this peripheral pressure anti-node which sun with the cehtr'al pressure anthracite Pi when the passage 23a is employed.

The domed upper combustion chamber wall 14 is similarly formed with entrance openings 30 and passages 31, leading to a centrally located chamber 32, the latter being closed at the top by a plug 33 screwed into a threaded port 34. The plug 33 will be seen to be hollow, and to have a reduced end extension 35 formed with gas ports 36 which are alighedwith the innermost ends of the passages 31'. Title cavity iiisid plug 33 is packed with a wad 37 of some suitable attenuative material, such as fiber glass. Access is gained to the cavity inside plug 33 by r cmovin'g a smaller plug 38 screwed iiitd the outer end of plug 33. As will be seh'; head 11 is open over plug 33, permitting the latter to be readily removed for scivicing; or plug 38 may be removed and access so gained to the fiber glass packing without first removing plug 33. V

In the present illustration the combustion chamber head wall structure is, for simplicity, shown only with gas passages for the two fundamental frequency pressure anti-nodes. Provision of additional passages for additional modes is within the capabilities of the designer, and will in any event depend upon the spacing of the pressure anti-nodes for any given combustion chamber design.

The total length and configuration of the two passages 23 connecting the two high impedance regions P for the fundamental mode, taken together with the shape and size of the chamber 24, are made such as to form a shunt gas passage between the regions P which is frequency responsive to the fundamental frequency acoustic wave pattern, thereby assuring gas oscillation in said shunt passage, as previously described. The fiber glass packing is a constricting means in the shunt passage giving high acoustic resistance.

For the first higher mode, the four passages 23 connecting the two high impedance regions P and the two high impedance region's P1 form the shunt passages; and for the third higher mode, the passages 23 conmeeting the two high impedance regions P and the four high impedance regions P3 form the shunt passages. If the shunt passages so formed are not sufiiciently short for good frequency response, the paths can be shortened by ihctcase in the size of the cavity 24 containing the fiber glass body. For sinner reasons, the length and cr'fifighidtibh oi the passage 23h (when used), together with" that of any one of the passages 23, should be such as to be frequency responsive to the frequericy of the second higher mode.

operation; the phenomena of detonation is ii'rcipic'nt when some portion of the fuel charge spontaneously explodes. This sets up acoustic waves in the high temperature and pressure gases in the combustion chamher, and the waves are found at high amplitude wave frequencies corresponding to resonant frequencies of the combustion chamber. As already explained, there may be one or a number of modes of vibration; each of which, hbwevcr, has ascei tainable regions of high acoustic impedance at which pressure anti-nodes tefid' to develop. The gas passage mouths 22 and 22a of the piston are located to coincide with these regions of high acoustic impedance for four typical modes of vibratioh, and the passages are thus connected in shunt between the high impedance re ions of the chamber. As already explained, the passages are designed to be frequency responsive to the modes or vibration to be attenuated, so that substantial oscillating gas flow occurs therein at the frequencies of the offensive acoustic waves iri the chamber. Further, as explained; this gas flow is at relatively high velocity. Because of the constriction of the passages by the fibrous packing material, the acoustic resistance of the passages is high, and the gas particles an accordingly caused to lose the majority of theii kinetic energy.

This energy drain is quite substantial, arid produces enough loss to prevent the build-up of the high amplitude pressure anti-nodes oth rwise eitperience'd within the combustion chamber. weakening of the resonant acoustic pattern for a pair of pressure anti-nodes, for any given mode of vibration, attenuates the entire acoustic pattern for that mode; and by this means, any one or all of the modes of vibration of a combustion chamber can be etfectivcly attenuated, and detohation correspondingly subdued.

In similar manner, oscillating gas flow is established in the passages 31 and through the fibrous packing 37, with like results. In practice, it may be sufl'lcient to utilize, because of convenience, only the piston form of the invention. For a still greater degree of control, the attenuation means of the invention may be used also in the head of the combustion chamber. It is also possible, of course, and of some definite advantage, because of ease of servicing, to use the attenuation means only in the head end of the combustion chamber.

Figure la shows a modification, wherein the gas pas sages are constricted by reduction of their transverse dimensions, rather than by use of packing material. In Figure la, a crowned piston 40 has entrance ports 41, understood to correspond with the entrance ports of the embodiment of Figure l in number and disposition. These ports are at the outer ends of gas passages 42 which radiate from a central point of iritercommunication, identified by the numeral 43. No packing material is employed, and the passages 42 in this instance are constricted to a transverse dimension of something of the order of .020 inch. This dimension is not necessarily critical, and is subject to variation in practice. The requirement is that the passages be suificiently constricted at their inner end portions to cause high velocity gas oscillation, and substantial crowding or compression of the oscillating high velocity gases. with resulting scrubbing action and dissipation of velocity energy. It should also be noted that in Figure la, the passages 42 are curved, rather than straight, as in Figure 1. With such curvature it is possible to employ a fiat top on the piston. Such a modification could also be made in the piston of Figure l. The general theory of operation of the modification of Figure 1a is the same as that described in connection with Figures l-3, the only difference being that in the case 01' Figure la, the constriction of the gas passages is obtained by reducing the transverse dimensions of the passages, rather than by interposing a body of packing material.

Figures 4 and 5 show another embodiment of the in vention, first disclosed in my aforementioned application Serial No. 252,818. In this instance, the piston only is illustrated. The piston, designated generally by numeral 50, has a head 51 beveled at the top, as at 52, and has formed in said head a plurality of exponential horn type passages 53, 54 and 55. In the illustrative example, the mouths of these horn type passages open through the beveled face 52 at substantial 45 spacings from one another. The mouths of the horns are thus located over a peripheral region of the piston, where the majority of the pressure anti-node zones are known to exist. By having two of the horn mouths at spacing, and a third midway between the first two, there is assurance of covering several known acoustic modes, as pointed out more fully in my aforesaid issued Patent No. 2,573,536. Briefly, as described in said patent, if two h'orn mouths are spaced apart by half the spacing distance of two known high impedance or pressure anti-node regions, then there is assurance of good coverage, since if one is too far removed from a high impedance zone to be effective, the other will then be sufiiciently close to be strongly effective. The horns 53, 54 and 55 extend generally horizontally through the piston head, but at different levels, so as not to intersect one another, and their small ends open through the beveled face 52 at of spacing from their entrance ends or mouths. The small ends of the passages are made to be sufliciently large in cross-section to provide some degree of acoustic coupling with the combustion chamber; typically, the diameters of the opening may be in the range of or thereabouts. With such acoustic coupling to the combustion chamber at both ends of the horn, gas oscillates in the horn passages in response to the pressure drive created by the high impedance pressure anti-node regions of the chamber with which the horn mouths and small end openings are made to approximately coincide. The gas oscillation occurring within the horn passages, particularly in the smaller end portion thereof, brings about the same type of gas scrubbing" effect referred to in connection with Figures 1-3 and, as previously explained, this gas scrubbing effect is dissipative of the acoustic energy which would otherwise be available to build up the harmful acoustic wave patterns sufficiently to produce serious detonation. With the acoustic energy bled away as described, the acoustic patterns do not build up to high amplitude, and the tendency to detonation is very greatly subdued.

Figures 6 to 8 show a further modified engine in accordance with the invention. Water cooled engine block 60 has cylinder 61 fitted with piston 62; and water cooled head 63 has intake and exhaust poppet valves, such as indicated at 64, operated by usual valve gear such as indicated at 65, and has, to one side of cylinder 61, a threaded port for spark plug 67. As will be seen, the highest portion of the combustion chamber 68 is adjacent the spark plug, and this portion of the combustion chamber, directly over an arcuate peripheral area of the piston, is extended upwardly into an exponential horn type attenuator generally designated by the numeral 70. The general theory underlying the horn type of attenuator is set forth in my aforementioned issued Patent No. 2,573,536, to which reference is here made. This attenuator 70 has a plug or body part 71, generally arcuate-shaped in section (see Figure 8), and received in a corresponding slot 72 extending vertically through head 63. At the top, the body 71 has a mounting flange 74, secured onto the head by screws 75. An exponential horn passage 80 is formed in this body 71, its mouth opening downwardly into the top of the combustion chamber, over the rim of the piston and adjacent the spark plug. The born 80 extends upwardly above mounting flange 74 into an extension 81, which thus contains the convergent throat of the horn. To the upper end of this extension 81 is connected one end of an attenuator tube 82, which for convenience, is coiled about extension 81, as indicated. The tube 82 is sufficiently long, typically 12 inches, so that the sound wave transmitted to it through the horn is conducted along the tube until it is almost completely dissipated.

As will be seen, the exponential horn passage 80 is not round in cross-section, but considerably flattened and bent into an are, so as to overlie an arcuate-shaped marginal or rim portion of the piston. lts arcuate extent is approximately 90, as best illustrated in Figure 8. The horn 80 in its mouth region is divided into a plurality of passages 80a, 80b, and 80c, by transverse webs 84.

It will be recalled that a typical acoustic wave pattern for the fundamental vibration frequency of a combustion chamber has two pressure anti-nodes located approximately diametrically across the combustion chamber from one another. The horn 80, with its mouth extending for 90 of angular extent about the chamber, is arranged to coincide closely enough with one such pressure anti-node region to assure an attenuative effect on the fundamental frequency, even though the locations of the pressure antinodes may not be precisely known, or may tend to shift. Thus, one end or the other of the horn mouth will either coincide or nearly coincide with a pressure anti-node region, or both ends will be sufficiently close to the two pressure anti-node regions to assure operation on the fundamental wave pattern.

In operation, taking into account first the fundamental wave pattern, sound waves proceed upward into the horn from the pressure anti-node region of the chamber, and because of the exponential shape of the horn, these waves are conducted through the horn and into the attenuator tube 82 without substantial reflection back. Within the relatively fine and lengthy attenuator tube 82, the energy of the sound wave accepted by the horn is almost complctely dissipated. it is of course necessary that the taper ratio of the horn be properly correlated with the fre quency and wave length of the fundamental sound wave frequency which is to be attenuated. This subject is fully discussed in my aforementioned patent, to which reference is here made.

The extended mouth of the horn is also effective to attenuate higher modes of vibration, where the pressure anti-nodes are relatively close spaced, as previously discussed herein and as diagrammed in Figure 3. Thus, the two outside passages 80a and 80b of the horn (see Figtires 7 and 8) may occupy locations in the general regions of two pressure anti-nodes of a higher frequency mode. The device as described has an attenuative effect on such higher frequency modes by the provision of a shunt pas sage consisting of the two passages 80a and 80b, and the communicating space within the horn above the upper edges of the webs 84. Operation is then substantially as described in connection with the embodiment of Figures 1 and 2, as described hereinabove. Briefly, combustion gases oscillate in the described shunt passage, and the passage is sufficiently constricted in one dimension (see Figure 6) as to provide high velocity gas oscillation together with frictional scrubbing of the gases, with consequent substantial energy dissipation.

The illustrative embodiment shows also a middle passage 80c, intervening between the passages 80a and 80b. For still higher modes, the passage 80c may cooperate with either the passage 80a or the passage 80b to form a constricted attcnuative shunt passage having an attenua tive effect on oscillating gas flow therethrough. The combination of the three passages 80a, 80b and She also provides accommodation and flexibility in the event that higher mode frequencies should shift about during operation.

Figures 9 and 10 show still another embodiment of the invention. Here a piston is formed in its head, and near its periphery, with an upwardly facing annular opening or mouth 91, and this annular opening 91 communicates with an annular passage 92 extending downwardly and radially inwardly to the center of the piston head. The cross-sectional area of this annular passage 92 converges in a radially inward direction in the manner of an exponential horn, and it will be seen that there is a common, constricted throat region at the center of the piston. This throat region has attenuative characteristics for sound waves by reason of its small, transverse dimension, but for greater attenuative effect I prefer to employ in that region a pad 93 of sound wave absorptive material, preferably fiber glass. For convenience in installing and servicing the pad 93, the piston head may be formed at its bottom with a threaded access opening 94 closed by a plug 95. Radially disposed ribs 96 Within the channel or passage 92 divide the latter into sectors 97, and function acoustically to provide separated sound wave passages extending in a radial direction, and at the same time function structurally to support the central disk portion 97 of the piston head from its remaining body portion below the channel 92. The ribs 96 also function as means for conducting heat from the disk portion 97 to the remainder of the piston.

In operation, the horn-shaped channel or passage 92 accepts sound waves of various modes and conducts them to the central throat region, where they are dissipated, either by reason of the constriction of the passage in that area or, more effectively, by the attenuative effect of the fiber glass packing 93. For certain modes of vibration, wherein a pair of opposed-phase pressure anti-nodes coincide with the annular opening at positions opposite two different sectors 97, of the sector-shaped passages formed by the dividing ribs 96, those two sectors, together with the central region containing the packing 93, may function to provide a shunt passage of high acoustic resistance, operating to attenuate the sound wave in the manner heretofore described.

The invention has now been described in several illustrative forms. It is to be understood, however, that this is for illustrative purposes only, and that various changes in design, structure and arrangement may be made Without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In an internal combustion engine having a combustion chamber therein defined by wall means including the top wall of a piston and wherein spaced regions of oppositely phased high acoustic impedance appear during combustion as a consequence of acoustic waves generated by the combustion at a resonant frequency of the chamber, a gas passage of high acoustic resistance in said wall means having its two ends exposed to said chamber and spaced apart and located so as to be in proximity to by the spacing distance between said spaced high impedance regions, said passage having a length and configuration acoustically tuning it for sound wave gas oscillation between said high impedance regions at said resonant frequency, all in such manner as to establish a tuned, energy-dissipative, shunt-connected gas oscillation passage with a velocity antinode between said regions of oppositely phased high acoustic impedance for said resonant frequency.

2. In an internal combustion engine having a combustion chamber therein defined by wall means including the top wall of a piston, and wherein spaced regions of oppositely phased high acoustic impedance appear during combustion as a consequence of acoustic waves generated by the combustion at a resonant frequency of the chamber, a gas passage in said wall means constricted in an intermediate region for high acoustic resistance, having its two ends exposed to said chamber and spaced apart and located so as to be in proximity to said high impedance regions, said passage having a length and configuration acoustically tuning it for sound wave gas oscillation through said intermediate region between said high impedance regions at said resonant frequency, all in such manner as to establish a tuned, energy-dissipative, shuntconnected gas oscillation passage having a velocity antinode region within said intermediate constricted region between said regions of oppositely phased high acoustic impedance for said resonant frequency.

3. In an internal combustion engine having a combustion chamber therein defined by wall means including the top wall of a piston, and wherein spaced regions of oppositely phased high acoustic impedance appear during combustion as a consequence of acoustic waves generated by the combustion at a resonant frequency of the chamber, a gas passage in said wall means having its two ends exposed to said chamber and spaced apart by the spacing distance between said high impedance regions, a fibrous packing in a central region of said gas passage to increase its acoustic resistance, said passage having a length and configuration tuning it for sound wave conduction at said resonant frequency, all in such manner as to establish a tuned, energy-dissipative, shunt-connected gas passage between said regions of oppositely phase high acoustic impedance for said resonant frequency.

4. A piston for use in the cylinder of an internal combustion engine within whose combustion chamber appear spaced regions of oppositely phased high acoustic impedance during combustion as a consequence of acoustic waves generated by the combustion at a resonant frequency of the chamber, said piston having a head with a gas passage having its two ends opening to the combustion chamber and spaced apart and located so as to be in proximity to said high impedance regions, said gas passage having a constriction in a region between its ends, and having a length and configuratioii acoustically tuning it for sound wave gas oscillation between said high im pedance regions at said resonant frequency, all in such manner as to establish a tuned, energy-dissipative, shuntconnected gas oscillation passage having a velocity antinode at said constriction between said regions of oppositely phased high acoustic impedance for said resonant frequency.

5. A piston for use in the cylinder of an internal combustion engine within whose combustion chamber appear spaced regions of oppositely phased high acoustic impedance during combustion as a consequence of acoustic waves generated by the combustion at a resonant frequency of the chamber, said piston having a head formed with a gas passage having its two ends opening to the combustion chamber and spaced apart by the spacing distance of said high impedance regions, a packing of fibrous material in said gas passage, and said passage having a length and configuration tuning it for sound wave conduction at said resonant frequency, all in such manner as to establish a tuned, energy-dissipative, shunt-connected gas passage between said regions of oppositely phased high acoustic impedance for said resonant frequency.

6. A piston having a crowned head formed near the periphery of its convex top surface with diametrically opposite ports interconnected through said head by a gas passage, and a body of fibrous material packed in said gas passage.

7. A piston having a head, and having formed in said head a constricted gas passage opening at its two ends to the combustion chamber of an engine through the upper side of said head, said ends of said passage being located near the periphery of the piston, and said constriction comprising a reduction of the gas passage to a small transverse dimension in the central region of the gas passage. v

8. A piston having a head, and having formed in said head a constricted passage opening at its two ends to the combustion chamber of an engine through the upper side of said head, said ends of said passage being located near the periphery of the piston, and said constriction comprising a fibrous packing body in the central region of said gas passage.

9. A piston having a head, and having formed in said head a constricted gas passage opening at its two ends to the combustion chamber of an engine through the upper side of said head, said ends of said passage being located near the periphery of the piston. said gas passage comprising two inwardly converging gas passage sections disposed radially of the piston. said piston having a cavity in communication with the inner ends of both of said gas passage sections, and a fibrous packing body lodged in said cavity.

l0. In an internal combustion engine having a combustion chamber wherein spaced regions of oppositely phased high acoustic impedance appear during combus tion as a consequence of acoustic waves generated by the combustion at a resonant frequency of the chamber. a head wall for said combustion chamber over the cylinder of the engine formed with a gas passage having its two ends exposed to the combustion chamber and spaced apart and located so as to be in proximity to said spaced high impedance regions. said passage having a constriction in area between its ends and having a length and configuration acoustically tuning it for sound wave gas oscillation between said high impedance regions at said resonant frequency, all in such manner as to establish a tuned, energy-dissipative, shunt-connected gas oscillation passage having a velocity antinode in the region of said constriction between said regions of oppositely phased high acoustic impedance for said resonant frequency.

11. The subject matter of claim 10, including a gas passage constricting means in the form of a body of fibrous material lodged in a cavity intersecting a central region of said gas passage.

12. In an internal combustion engine having a combustion chamber therein defined by wall means including the top wall of a piston, and wherein spaced regions of oppositely phased high acoustic impedance appear during combustion as a consequence of acoustic waves generated by the combustion at a resonant frequency of the chamber, a horn passage in said wall means tapering substantially in accordance with an exponential law, said horn passage having its mouth in communication with the combustion chamber, with two regions of the horn mouth spaced apart by the spacing distance of said spaced regions of high acoustic impedance, and divider means in the mouth of said horn between said two regions of the horn mouth, said divider means extending inwardly of the born to a region where the horn passage is materially constricted, all in such manner as to provide a constricted shunt passage extending between the two said regions of the horn mouth and comprising the horn passage spaces on opposite sides of said divider means and the constricted region in the horn inwardly of said divider means.

13. For use with an internal combustion engine having a combustion chamber and a cylinder opening into said chamber, said chamber developing an acoustic wave pattern owing to detonation, said pattern having regions of oppositely phased high acoustic impedance, :1 piston adapted for reciprocation in said cylinder, and a sound wave conduit in said piston having the two ends thereof opening through the piston into said chamber, said conduit opening into the combustion chamber in said regions oi oppositely phased high acoustic impedance in the combustion chamber, said conduit being acoustically characterized by high acoustic resistance at the wave frequency of detonation.

14. A piston having a head, and having formed in said head a gas passage opening at its two ends to the combustion chamber of an engine through the upper side of said head, said ends of said passage being located near the periphery of the piston, said two gas passage sections converging inwardly, and having a constricted communicating region with one another at their inner ends, and being flared at their outer end portions.

15. In an internal combustion engine having a combustion chamber therein defined by a wall means including the top wall of a piston, and wherein spaced regions of oppositely phased pressure anti-nodes appear during combustion as a consequence of acoustic waves generated at a resonant frequency of the chamber, a shunt gas passage of high acoustic resistance extending through said wall means having its two ends opening to said chamber in proximity to said pressure anti-nodes, said passage having a iength and configuration adjusting it for acoustic response to the resonant frequency of said chamber, whereby substantial gas oscillation takes place in said shunt passage under drive by said oppositely phased pressure anti-nodes.

References Cited in the file of this patent UNITED STATES PATENTS 1,818,339 Lang Aug. 11,1931 1,913,310 Moore June 6, 1933 2,017,748 Bourne Oct. 15, 1935 2,151,218 Lutz Mar. 21, 1939 2,206,322 Huesby July 2, 1940 2,256,776 Kammer Sept. 23, 1941 2,402,213 Starr June 18, 1946 FOREIGN PATENTS 483,762 Germany Oct. 5, 1929 500,023 Germany June 16, 1930 676,997 Germany June 16, 1939 736,047 Germany June 5, 1943 390,596 Great Britain Apr. 13, 1933 442,598 Great Britain Feb. 11, 1936 34,347 France May 4, 1929 (First addition to No. 63 6,154) 868,056 France Dec. 15, 1941 

